1. Field of the Invention
The present invention relates to a lubricating system for friction engaging means in a power shift transmission and more specifically to a lubricating system for clutches and/or brakes therein.
2. Background of the Invention
An example of friction engaging means (clutch) lubricating systems of this kind is disclosed in Japanese Utility Model Kokai Publication No. 53-15478, in which a working fluid drained from a torque converter turbine is cooled through a cooling unit, pressure-regulated through a check valve, and then supplied to all the friction engaging means (clutches, etc.) incorporated in a power shift transmission.
3. Discussion of the Prior Art
In the above conventional lubricating system for friction engaging means, however, since the lubricant is simply supplied to all the friction engaging means without adjusting the quantity of the lubricant to be supplied to each friction engaging means according to each transmission shift position, it has been necessary to always supply the maximum necessary quantity of lubricant to each friction engaging means, thus resulting in problems in that an oil pump of a large capacity should be provided for securely supplying the maximum necessary quantity of lubricant, or else there arises a serious accident such as clutch seizing.
Suppose a transmission with each one speed range of FORWARD and REVERSE. Here, if the above-mentioned maximum necessary quantity of lubricant is secured, even when the transmission is shifted to NEUTRAL, for instance, there will not occur such a problem that a vehicle is started at NEUTRAL shift position by a slip torque under the condition that the quantity of lubricant supplied to the FORWARD clutch (i.e., clutch taking part in establishing FORWARD) is the same as that supplied to the REVERSE clutch (i.e., clutch taking part in establishing REVERSE). However, there still exists a problem in that, when the vehicle is driven in the forward or rearward direction, the transmission efficiency is lowered due to an increase in the slip torque caused by the other disengaged friction engaging means (clutch or brake).
Further, in the case of a transmission with two FORWARD ranges and one REVERSE range, if the same quantity of lubricant is supplied to the three friction engaging means, there exists a problem such that a slip torque is produced in the forward direction at the NEUTRAL position and the transmission efficiency is lowered due to the slip phenomenon in each transmission shift position.